One type of electromechanical actuator for influencing sewing machine stitch patterns operates in association with a servo-system comparing input signals related to the stitch pattern being executed with reference signals related to the existing position of the actuator. A conventional potentiometer comprising a coil with a wiper having contact relatively movable along the coil and functioning as a voltage divider would involve distinct disadvantages when utilized to provide positional reference signals for such a sewing machine actuator. Wear occurring because of the contact between the parts can be troublesome, especially since extended periods of sewing machine operation occur in particular positions such as the straight stitch position and because of dither motions occurring in such frequently used positions the conventional potentiometer will wear quickly at certain points.
Those non-contact position sensing devices which are known for use other than in sewing machine applications, would not serve satisfactorily in place of the device of the present invention for one or more of the following reasons:
Known non-contact position sensing devices involve high inertia effects which would be detrimental to the effective operation of the electromechanical sewing machine actuator.
Known non-contact position sensing devices do not exhibit sufficiently linear response ranges.
Known non-contact position sensing devices generate objectionable radio interference.
The large size of known non-contact position sensing devices and the requisite shielding required with them would require inordinately large space and such devices would not be adapted for accommodation within the crowded space available within a sewing machine frame.